"There's been confirmed a number of senior people who were coming out here who were researchers, who were medical scientists, doctors, people who've been to the forefront of dealing with AIDS across the world," Victoria Premier Denis Napthine told reporters in Melbourne on Friday. "The exact number is not yet known, but there is no doubt it's a substantial number."

The Australian newspaper reported that up to 108 delegates to the 20th International AIDS Conference in Melbourne, which starts Sunday, are believed to have died on flight MH17.

The International AIDS Society issued a brief statement Thursday night saying that "a number of colleagues and friends" were on the flight.

"At this incredibly sad and sensitive time the IAS stands with our international family and sends condolences to the loved ones of those who have been lost to this tragedy," the statement said.

Unconfirmed reports suggest that among the dead are researcher Joep Lange, of the University of Amsterdam, and World Health Organization spokesman Glenn Thomas.

Lange is well known in the field, with dozens of publications. He led clinical trials involving antiretroviral therapies, and the prevention of mother-to-child transmission of HIV. He was president of the International AIDS society from 2002-2004, and is a founder and co-editor-in-chief of the journal Antiviral Therapy.

Chris Beyrer, president-elect of the IAS, said that if reports of Lange's death were true, "then the HIV/AIDS movement has truly lost a giant."

According to his Linked-In profile, Thomas had been a spokesperson for the WHO since March 2003, and had spent five years as a BBC News producer before that.

Separately, the International HIV/AIDS Alliance confirmed the names of two other Dutch victims: Pim de Kuijer, a lobbyist at the group Stop AIDS Now, and Martine de Schutter, a program manager at Bridging the Gaps, an organization that lobbies for universal access to HIV prevention.

De Schutter, who had lived in Argentina, Bolivia and the United States, in addition to the Netherlands, was a cultural anthropologist specializing in gender, sexual and reproductive health, including AIDS.

"Pro-active defence of human rights and the right to good health is at the core of my work," she wrote in her Linked-in profile. "Throughout my (professional) life I hope to contribute to making the world a better place to live, work and love."